The invention relates to a structural component having a twisted profile and to a method and apparatus for producing such a structural component, especially a large scale structural component such as the wings of a windmill or a helicopter rotor blade. Such structural components have two portions which are intimately bonded to each other along an interface surface.
It is known to use a foam material in the construction of helicopter rotor blades for providing a load take-up structure and for transferring shearing forces as well as torsion loads. A foam material known under the tradename "Conticell 40" is suitable for this purpose. Since the wing depth measured vertically and perpendicularly to the longitudinal axis of a helicopter rotor blade or wing is constant over substantial portions of the rotor blade length, for example, over the entire profiled portion of the wing, it is possible to use a so-called profile cylinder of foam material which is also referred to as a foam core. In helicopter rotor blades the use of such a foam core is further facilitated by the fact that the blade construction is substantially constant or uniform over the mentioned range. Merely at the wing tip is it necessary to use a foam core potion having the shape of a profiled cone. However, such profiled cone makes the production substantially more difficult because it requires, for example, so-called copy milling by a machine tool.
Further, in a relatively small helicopter rotor wing there is no interface between two portions of the wing because the shape of the wing is determined by the compression resulting from moving two mold halves together at a time when the laminations impregnated with a resin material are still moist or at least at a time when the curing of the resin material merely resulted in a gel type consistency.
On the other hand, in connection with large scale structural components such as windmill wings, wings for glider airplanes, and large helicopter blades, the foam core must be replaced by a shearing member capable of taking up the high shearing forces to which such large scale structural components are exposed during operation. Such shearing member has been shaped heretofore by manual operations, for example, sanding operations, in order to adapt the shape of the shearing member to the shape of the upper and lower shell of the respective wing. Manufacturing steps performed by hand may be acceptable where the number of components to be produced is relatively small, and further provided that the size of the structural component involved is still manually managable. However, where larger production numbers are involved or where the size of the structural component becomes too large for manual operations, the prior art does not provide any solutions to the problems involved under such circumstances.
Furthermore, in connection with large scale rotor blades as they are used, for example, in wind energy converters comprising windmills, it is desirable to use a foam core even in such large scale components in order to reduce the weight of the rotor structure as long as the shearing loads are small enough to be handled by a foam core. However, due to the large size of such blades, it is necessary to first manufacture the blade in two portions, for example, as an upper shell and a lower shell which are then intimately bonded to each other along an interface formed by the two separation surfaces of the two wing portions. These separation surfaces require a precision machining prior to the bonding so that an intimate bonding is assured along the surface of the entire interface. Due to the large twisting of such a blade along its length, it is necessary that the mentioned interface and thus also the two separation surfaces which after the bonding form the interface, are also having the same twisting.
Heretofore, it has been difficult, time consuming, and hence expensive to properly machine these separation surfaces forming the interface between the two blade portions. Especially to be mentioned is the substantial control apparatus required for such machining. Furthermore, large tolerances had to be accepted due to angular errors. Additionally, the machine tool set up required a substantial number of man hours to be performed by highly skilled tool setters. Moreover, the manufacturing control required a substantial measuring effort involving the use of precision measuring techniques and equipment.